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# layout of boot.img
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### 1. header part
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item size in bytes
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+----------------------------------------------------------+
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|<MAGIC HEADER> | 8 |
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|--------------------------------+-------------------------|
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|<kernel length> | 4 |
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|--------------------------------+-------------------------|
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|<kernel offset> | 4 |
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|--------------------------------+-------------------------|
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|<ramdisk length> | 4 |
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|--------------------------------+-------------------------|
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|<ramdisk offset> | 4 |
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|--------------------------------+-------------------------|
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|<second bootloader length> | 4 |
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|--------------------------------+-------------------------|
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|<second bootloader offset> | 4 |
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|--------------------------------+-------------------------|
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|<tags offset> | 4 |
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|--------------------------------+-------------------------|
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|<page size> | 4 |
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|--------------------------------+-------------------------|
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|<header version> | 4 |
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|--------------------------------+-------------------------|
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|<os version& os patch level> | 4 |
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|--------------------------------+-------------------------|
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|<board name> | 16 |
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|--------------------------------+-------------------------|
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|<cmdline part 1> | 512 |
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|--------------------------------+-------------------------|
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|<hash digest> | 32 |
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|--------------------------------+-------------------------|
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|<cmdline part 2> | 1024 |
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|--------------------------------+-------------------------|
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|<dtbo length> | 4 |
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|--------------------------------+-------------------------|
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|<dtbo offset> | 8 |
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|--------------------------------+-------------------------|
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|<header size> | 4 |
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|--------------------------------+-------------------------|
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|<padding> | min(n * page_zie - 1648)|
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+----------------------------------------------------------+
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### 2. data part
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+----------------------------------------------------------+
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|<kernel> | kernel length |
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|--------------------------------+-------------------------|
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|<padding> | min(n * page_zie - len)|
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+----------------------------------------------------------+
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+--------------------------------+-------------------------+
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|<ramdisk> | ramdisk length |
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|--------------------------------+-------------------------|
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|<padding> | min(n * page_zie - len)|
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+----------------------------------------------------------+
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+--------------------------------+-------------------------+
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|<second bootloader> | second bootloader length|
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|--------------------------------+-------------------------|
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|<padding> | min(n * page_zie - len)|
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+----------------------------------------------------------+
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+--------------------------------+-------------------------+
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|<recovery dtbo> | recovery dtbo length |
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|--------------------------------+-------------------------|
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|<padding> | min(n * page_zie - len)|
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+----------------------------------------------------------+
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### 3. signature part
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#### 3.1 Boot Image Signature (VBoot 1.0)
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+--------------------------------+-------------------------+
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|<signature> | signature length |
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|--------------------------------+-------------------------|
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|<padding> | defined by boot_signer |
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+----------------------------------------------------------+
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#### 3.2 AVB Footer (VBoot 2.0)
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+--------------------------------+-------------------------+
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|<signature> | signature length |
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|--------------------------------+-------------------------|
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| ... | ... |
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|<padding> | defined by avbtool, |
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|<padding> | it will pad to requested|
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|<padding> | image size |
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| ... | ... |
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+----------------------------------------------------------+
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